The present invention relates to a multilayer injection molding machine capable of press fitting resins from a plurality of injection units to a cavity part within a metal mold, respectively, an injection unit connecting device therefor, and an injection molding method thereby.
In the manufacture of molded product formed of a plurality of layers of resins or colors, an injection molding machine for press fitting the resin of each layer into a metal mold in order is generally adapted, but in recent years, a multilayer injection molding machine capable of press fitting the resins of all the layers into the metal mold by one operation has been developed and adapted so that the molding time can be shortened to improve the productivity.
The conventional multilayer injection molding machine is constituted, as shown in FIG. 6, by juxtaposing, every resin of each layer, a plurality of (for example, two) injection units 53, 53 each of which has a heating cylinder 51 capable of raising the internal temperature to a prescribed temperature or more and an extruding screw 52 provided rotatably within the heating cylinder 51, and connecting and integrating the injection units 53, 53 together through a nozzle member 54. In injection molding, the tip of the nozzle member 54 is brought into contact with the spool hole of a metal mold 55, and the resin from each injection unit 53, 53 is then collected together in the nozzle member 54 and discharged through the tip, whereby the resin of each layer is simultaneously press fitted into the metal mold 55.
However, since the above-mentioned conventional structure having all the injection units 53, 53 connected and integrated to the nozzle member 54 is intended for an exclusive machine for a molded product having the number of layers corresponding to the number of units of the injection units 53, 53, it is required to introduce and set a multilayer injection molding machine for every molded product having each number of layers. Thus, even if a single-layer injection molding machine, for example, was introduced, new introduction of a two-layer injection molding machine is necessary in addition to this machine when a two-layer molded product is required. Therefore, existing facility equipments such as an injection molding machine, carrying device, and the like can not be effectively utilized. In a factory having no sufficient setting space, particularly, the introduction is extremely difficult since an action such as layout change of each equipment or disposal of the existing injection molding machine with the lowest frequency of use is required in order to ensure the setting space.
In recent years, it is also desired, form the view point of material cost or effective use of resources, to manufacture a molded product in which a core layer resin of low quality or low cost is thoroughly or partially covered with a desired skin layer resin. Thus, the multilayer injection molding machine having the structure described above is used also to cover such a core layer resin with the skin layer resin. However, this molding machine has a problem in that it is difficult to more surely cover the core layer resin with the skin layer resin because the core layer resin is likely to be included to the skin layer resin at the start of press fitting.
Thus, an object of the present invention is to easily manufacture a molded product having an optional number of layers by use of existing facility equipments.
Further, another object of the present invention is to surely cover a core layer resin with a skin layer resin in the manufacture of a molded product having the core layer resin covered with the skin layer resin.